1. Field of the Invention
The present invention relates to an expansion valve and an air conditioner for vehicles having the same, and more particularly, to an expansion valve, which can branch and expand refrigerant supplied from a condenser, discharge the branched and expanded refrigerant to an evaporator, and differently control the degree of opening of first and second orifices through first and second valves varied in their positions by a single shaft, and an air conditioner for vehicles having the expansion valve.
2. Background Art
In general, an air conditioner for vehicles is an auto part, which is installed in a vehicle for the purpose of cooling or heating the interior of the vehicle in the summer season or the winter season or removing frost from a windshield in the rainy season or the winter season to thereby secure a driver's front and rear visual fields. Such an air conditioner typically includes a heating device and a cooling device together, so that it can heat, cool or ventilate the interior of the vehicle through the steps of selectively introducing the inside air or the outside air into the air conditioner, heating or cooling the introduced air, and blowing the heated or cooled air into the vehicle.
As shown in FIG. 1, a typical refrigeration cycle of the air conditioner includes a compressor 1 for compressing refrigerant, a condenser 2 for condensing the refrigerant of high pressure sent from the compressor 1, an expansion valve 3 for throttling the condensed and liquefied refrigerant, and an evaporator 4 for evaporating the liquid refrigerant of low pressure throttled through heat exchange with the air sent to the interior of the vehicle to thereby cool the air discharged to the interior of the vehicle due to the heat absorption effect by latent heat of the refrigerant, and the compressor 1, the condenser 2, the expansion valve 3 and the evaporator 4 are connected with one another in order via a refrigerant pipe 5. The interior of the vehicle is cooled through the following refrigerant circulation process.
When a cooling switch (not shown) of the air conditioner is turned on, the compressor 1 is first operated by engine power to thereby inhale and compress refrigerant gas of low temperature and low pressure and send the refrigerant gas to the condenser 2 in a high temperature and high pressure state, and then, the condenser 2 heat-exchanges the refrigerant gas with the outside air to thereby condense it into liquid refrigerant of high temperature and high pressure.
The liquid refrigerant of high temperature and high pressure sent from the condenser 2 is rapidly expanded by a throttling action of the expansion valve 3 and sent to the evaporator 4 in a saturated vapor state of low temperature and low pressure, and then, the evaporator 4 heat-exchanges the refrigerant received from the expansion valve 3 with the air blown to the interior of the vehicle by a blower (not shown)
Continuously, the refrigerant evaporated through heat-exchange with the outside air in the evaporator 4 is discharged in a gas phase of low temperature and low pressure and inhaled again into the compressor 1, and then, recirculated through the above-mentioned refrigeration cycle.
In the above refrigerant circulation process, cooling of the interior of the vehicle is achieved in such a way that the air blown by the blower (not shown) is cooled by the latent heat of the liquid refrigerant circulating in the evaporator 4 while passing through the evaporator 4 and discharged to the interior of the vehicle in a cooled state.
In the meanwhile, a receiver drier (not shown) for separating the refrigerant in a liquid phase from the refrigerant in a gas phase is mounted between the condenser 2 and the expansion valve 3 so as to supply only the refrigerant in the liquid phase to the expansion valve 3.
However, because the refrigeration cycle has a limit in improving the cooling efficiency, as shown in FIG. 2, a multiple-effect evaporation system for improving the cooling efficiency through multiple-effect evaporation has been developed.
The multiple-effect evaporation system shown in FIG. 2 includes two evaporators 4a and 4b arranged side by side, wherein refrigerant passing through one expansion valve 3 is branched and respectively supplied into the evaporators 4a and 4b. 
Now, referring to FIG. 3, the expansion valve 3 will be described in brief. The expansion valve 3 includes: an orifice 34 formed between an inflow channel 32 and an outflow channel 33 on a lower portion thereof for expanding the refrigerant received from the condenser 2 and supplying it to the evaporators 4a and 4b; a main body 31 mounted on an upper portion thereof and having a connection channel 37 for supplying the refrigerant discharged from the evaporators 4a and 4b into the compressor 1; a valve 35 for controlling a flow rate of the refrigerant passing through the orifice 34; and a shaft 38 slidably moving by a diaphragm 36, which is varied in its position according to a temperature change of the refrigerant flowing inside the connection channel 37, to thereby move the valve 35.
Therefore, the first evaporator 4a located on an upstream side in an air flowing direction first cools the air, and then, the second evaporator 4b second cools the first cooled air, whereby the cooling efficiency is improved.
However, the multiple-effect evaporation system has a problem in that because the expansion valve 3 has just one orifice (expansion channel) 34, which equally branches the refrigerant expanded by and discharged from the expansion valve 3 and respectively supplies the branched refrigerant into the two evaporators 4a and 4b, it cannot differently control refrigerant flow rates of the refrigerant supplied to the two evaporators 4a and 4b. 
That is, the first evaporator 4a located on the upstream side in the air flowing direction receives relatively less load than the second evaporator 4b because warm air is introduced into the first evaporator 4a, but the second evaporator 4b receives relatively more load than the first evaporator 4a because the air first cooled in the first evaporator 4a is introduced into the second evaporator 4b. Hence, there is a need to differently control the refrigerant flow rates supplied to the evaporators 4a and 4b according to load applied to the two evaporators 4a and 4b. However, the expansion valve 3 of the multiple-effect evaporation system shown in FIG. 2 cannot differently control refrigerant flow rates supplied to the two evaporators 4a and 4b. 
Accordingly, the multiple-effect evaporation system having the expansion valve 3 according to the prior art still has a limit in improving the cooling efficiency.
Meanwhile, as shown in FIG. 4, another evaporation system having two evaporators 4a and 4b and two expansion valves 3a and 3b for differently controlling refrigerant flow rates toward the evaporators 4a and 4b is disclosed. But, such an evaporation system also has several problems in that it needs a wide space, has a complicated structure, and increases manufacturing expenses due to an increase of the number of components because the two expansion valves 3a and 3b are mounted therein.